I came across another example today of two adult Lesser Black-backed Gulls (Larus fuscus) displaying choking behavior, possibly as an act of aggression rather than pair bonding (I would not expect to see adults still having to confirm their bond at this stage of the breeding season). I witnessed the scene near a resting place on the outskirts of the city center.
Interestingly, today as well as on recent occasions that I have witnessed (aggressive) choking behavior, it was performed near a tree or a lamp post. For some reason, such objects are included in this ritual whenever possible.
See for example this video (taken in August 2012 and part of an article I wrote last year about adult Lesser Black-backed Gulls pairing up after the breeding season):
It’s the same in the USA as well (taken in San Diego, California in April 2013, here the ritual is pair bonding):
To find out more about this behavior, see Gull behavior explained: choking.